Low tension sparking plug



May 9, 1950 w. B. SMITS LOW TENSION SPARKING PLUG Filed Dec. 6, 1946 Patented May 9, 1950 UNITED STATES PATENT OFFICE Application December 6, 1946, Serial No. 714,483 In the Netherlands December 14, 1945 The invention relates to a low tension sparking plug, the electrodes of which are separated by electrically insulating or semi-conductive solid material, on the surface of which the igniting spark is produced. The sparks of those sparking plugs have a very high intensity and affect not only the material of theelectrodes but also the solid material separating, the electrodes. That is why sparking plugs of this kind do not last long.

The invention has for its object to provide a sparking plug which lasts considerably longer than known plugs of this kind. It consists in this, that the electrodes are shaped in such a manner, that their active surfaces enclose a, preferably acute, angle and so diverge in the direction from the separating material between the electrodes to the outside, that a groove or recess is formed, on the bottom of which the igniting sparks are produced. It has been found that in this construction the sparks, immediately after their production, are blown out of the groove or recess between the electrodes by a great force probably exerted by the sudden expansion of the intensively heated gas surrounding them. Consequently, the sparks hardly come into contact with the separating material, so that the latter is saved from destruction.

Advantageously the electrodes are made of material having a great heat conductivity, such as copper, silver or an alloy of each of the two metals. In that case the electrodes, by their good heat conduction, remain relatively cold on the spots, on which the sparks are produced.

In some cases a further improvement is obtained when the active surface of the electrodes are galvanized, or similarly treated in order to acquire a better heat resistance thereof.

It may also be of advantage to place a thin washer of heat resisting material between the head of the central electrode and the insulating or semi-conductive member separating the electrodes.

For the elucidation of the invention reference is had to the accompanying drawing, illustrating by way of example an embodiment of the invention. In the drawing:

Figs. 1 and la are respectively a longitudinal sectional view and a bottom view of a composite element of electrodes, the active surfaces of which form a groove having diverging side-walls.

Fig. 2 a longitudinal sectional View of a sparking plug having a composite element of electrodes as shown in Figs. 1 and 1a.

In the drawing I designates an annular outer 2 Claims. (CL 123-169) electrode of good heat-conducting material such 68 as copper. This electrode is separated from a central electrode 3 by a tubular member 2 of electrically insulating or semi-conductive material. The inner surface of electrode I is conically shaped. The tubular member 2 has a correspondingly conical outer surface. The electrodes l and 3 and the separating member 2 are pressed together by a great force exerted by means of an insulator 4, a washer 5 and nuts 6 and I mounted and screwed respectively on the central electrode. The spaces between the insulator 4, the electrode I and the separating member 2 are filled with elastic material 8, which closes the joints between the various parts of the sparking plug in an air-tight manner. Packingmaterial 9 is also provided between the insulator 4 and the washer 5. The central electrode 3 has a head, the periphery IU of which constitutes the active surface. The outer electrode i has been worked out conically and has an active surface H. The active surfaces It! and H enclose an angle of about 30, so that a groove or recess is provided, the bottom of which consists of electrically insulating or semi-conductive material. The sparks are produced on this bottom. However, they are blown out of the groove immediately after their production.

The active end of the outer electrode l is slotted as shown at l2 in order to render this end slightly resilient and to prevent the separating member 2 from being pressed too strongly.

The composite element of electrodes according to Figs. 1 and 1a. is mounted in a plug body 13 (Fig. 2), which is provided with a leading-in in sulator 14 for the electrical connection of the sparking plug.

It will be often of advantage to provide a thin washer l5 of electrically conductive and very well heat-resisting material under the head of central electrode 3 (Fig. 1).

It may be noted that the invention may be applied as well in sparking plugs, the electrodes and the separating member of which are assembled to a firm unity by melting or sintering, in such a manner, that gaps between adjacent parts are avoided.

What I claim is:

1. Low tension spark plug, comprising concentric electrodes and a member of electrically at most semi-conductive solid material, on the surface of which the sparks are produced, said member separating the electrodes, and said electrodes being shaped in such a manner that the active surfaces thereof enclose an angle of at most 30 and so diverge in a direction from said separating member to the end face of the plug, that in said end face a circular groove is formed on the bottom of which the igniting sparks are produced.

2. Low tension spark plug as claimed in claim 1, comprising a central electrode, a head provided on said electrode, and a thin washer of heatresisting electrically conductive material mounted between said head and the separating member.

WYT'ZE BEYE SMITS.

REFERENCES crrEn Number Number UNITED STATES PATENTS Name Date Ransomer Mar. 16, 1920 mew/er May 25, 1920 Hurley June 10, 1930 Parkin June 12, 1934 Smits July 26, 1938 Abell July 14, 1942 FOREIGN PATENTS Country Date oreetiiamam Jan. 17, 1929 Italy Jan. 13, 1937 

